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Abstract

The color of a material, such as solution of a dye, can change by changing parameters like pH, temperature, illumination direction, and illumination type. Dichromatism—a color change due to the difference in thickness of the material—has long been known as a property of only a few materials. Here we show that dichromatism is a common property of many substances and materials, and we introduce a method for its quantification. We defined dichromaticity index (DI) as the difference in hue angle (Δhab) between the color of the sample at the dilution, where the chroma is maximal, and the color of four times more diluted (or thinner) and four times more concentrated (or thicker) sample. The two hue angle differences are called dichromaticity index toward lighter (DIL) and dichromaticity index toward darker (DID), respectively. High dichromaticity was found for materials that were previously known as dichromatic (pumpkin oil, bromophenol).

References

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Table 1

Dichromaticity (DIL and DID) and Related Parameters of Selected Substances, Calculated from Their VIS Absorption Spectra by the Computer Algorithm Dichromaticity Index Calculatora

Substance

DIL

DID

ChromaL

ChromaMAX

Angle @ ChromaMAX

ChromaD

1,1-diethyl-2,2-cyanine iodide

4.29

−1.14

98.60

107.07

44.61

90.56

acridine orange

−10.14

−17.89

105.62

118.43

88.30

94.04

acridine yellow

−2.09

−1.68

118.93

123.14

98.58

115.03

auramine O

−3.37

0.39

124.79

130.14

94.68

119.41

beta carotene

−5.66

−7.00

114.41

131.81

91.54

121.65

bilirubin

−4.65

−6.03

132.34

136.45

90.33

128.17

bromophenol blue pH 3.0

−12.41

−31.11

70.20

107.55

86.58

77.84

bromophenol blue pH 3.2

−14.58

−42.44

56.91

92.85

86.52

76.21

bromophenol blue pH 3.4

−48.92

−14.09

71.00

74.50

37.83

55.44

bromophenol blue pH 3.6

−51.38

−16.38

53.79

70.62

37.40

49.50

bromophenol blue pH 3.8

−49.76

−18.30

31.13

65.47

34.26

40.74

bromophenol blue pH 4.0

−26.53

−10.82

20.81

68.92

31.44

49.64

bromophenol blue—water

−12.95

−34.68

66.70

104.68

86.39

80.05

C3 indocyanine

8.21

17.27

68.53

89.34

348.03

85.86

chlorophyll a in ether

29.23

60.67

34.95

50.39

201.38

34.46

chlorophyll b

11.18

27.28

32.64

44.51

143.23

29.59

coumarin6

−1.95

−0.26

126.93

131.21

96.47

124.29

coumarin343

−1.91

−0.03

115.69

120.93

99.60

112.86

cryptocyanine

37.90

1.94

66.65

84.31

301.27

44.10

crystal violet—glycerol

9.66

3.32

96.83

141.29

318.33

106.33

crystal violet—water

9.31

3.67

99.39

141.98

319.06

107.98

fluorescein dibase

−1.59

−6.94

91.23

120.36

75.44

88.76

hemoglobin—oxy

−1.17

−5.63

63.09

108.37

42.60

88.78

hemoglobin

−2.34

−5.89

35.83

62.27

19.03

24.84

malachite green

7.32

24.41

41.70

61.23

223.21

49.74

nile blue—methanol

34.93

7.76

65.95

78.34

288.93

44.14

nile red

18.51

−9.46

82.43

103.22

45.91

69.28

proflavin pH 7

−6.13

−10.64

88.81

101.60

98.53

84.30

pumpkin oil

−8.97

−44.12

37.19

59.84

102.17

40.87

resazurin

33.16

40.61

22.96

36.18

331.27

6.15

rhodamine 6G

21.89

−0.82

84.27

110.46

54.37

85.99

vitamin B12

34.82

−6.22

76.73

102.00

39.82

79.31

aChromaMAX: maximal chroma, ChromaL: chroma at four times more diluted solution, ChromaD: chroma at four times more concentrated solution, Angle @ ChromaMAX: the hue, which is represented by the angle of the vector to the color with maximal chroma in the CIELAB colorspace diagram.